x 
58 J. W. Bailey on a Universal Indicator for Microscopes. 
Arr. VI.—On a Universal Indicator for Microscopes ; by Prof. : 
J. W. Bawey, U.S. Military Academy.— With a Plate. 
In the Quarterly join of Microscopical Science, vol. i, p. 34, 
an ingenious contrivance for registering the position of microscopi¢e 
objects is described by Mr. Tyrrel; a modification of this, 
r. Aymot is given in a subsequent number (l..c., vol.i, p. 301); 
and a still better arrangement for the same purpose, suggested by 4 
Mr. Brodie and applied by Mr. Okeden to his microscope, is de- | 
“ seribed at p. 166 of volume iil. of the same work. The last men- 
tioned device can scarcely be improved upon for convenience ; 
but we is one defect which is inherent to all these inventions, 
that they are essentially selfish contrivances, of no use to 
put ge owner of the particular instrument to which they 
The ree of the instrument I propose is more comprehensive 
“Finders” above alluded to; being no less than 
to make a Unive sal Indicator by means o ‘whic an observer 
can so register the position of “los number of objects mounted 
upon slides, that when these are s 
the latter may be able by meat c 
= of these objects as easily as if he had 
jects shall then be entirely inlepeuiiant of the original instr 
ment and observer, and applicable to any microscope, it will te 
to promote science not only by facilitating the interchange of 
——— among naturalists, but it will give to each observer’s col- 
lection when properly registered, a ewe scientific value and 
utility which it could have in no other m 
The plan I have adopted is to make upon an engraved card 
what may be considered as a transferable stage having guide 
lines by meansof which the centre of the field of view of the 
microscope, and the position of a slide when any object upon it 
occupies this centre, may be giv: 
Plate I. shows the Indicator complete, The centre of the field — 
of view corresponds to the intersection of the horizontal line C,D, 
with the vertical line E, F. On the right and left hand of this — 
centre the vertical axes B, and A’, are placed at distances of {ths 
of an inch, and the axes A, and B’ are ee placed at the ‘dis- 
tances of ths of an inch from the ce 
The axes are then graduated as seen in the plate; the smal 
divisions being each ;';th of the standard inc 
The dotted lines Gg ‘A, I, give the outline of whet: will be t rer 
ferred to as the centre piece. 
